I fired a 1911 a1 RR for the frist time.On the Frist clip fired the slide styed open after last shot . ON the next four clips fired the slide remaned closed after the last shot and the hammer was in the cocked position.Can someone explain what happened?
The mag follower might have jumped the slide stop notch. If the slidestop wasn't engaged by the follower, the slide just closed because the slide stop wasn't pushed far enough up to catch the slide notch.
On the occassions when the slide was closed after the last shot, did the mag drop freely when you tried to eject it, or did you have to manually pull it from the gun? If the latter, the problem is as mentioned above. If the mag dropped out normally, it could be that the mag spring is weak, or the follower is bent in such a way that it doesn't properly engage the slide stop.
Try racking the slide manually, with the empty mag in place. Look into the ejection port, and watch how the slide stop and mag follower interact; you should either see the follower slip past the slide stop, or the follower not exerting sufficient pressure to lift the slide stop.